The present invention relates to an electron emitting device for emitting electrons and a method for producing the same, and in particular to an electron emitting device produced using particles containing a carbon material having a carbon six-membered ring structure or an aggregate thereof, and a method for producing the same. The present invention also relates to an electron emitting source including a plurality of such electron emitting devices, an image display apparatus utilizing such an electron emitting source, and a method for producing them.
Recently, micron-size electron emitting devices have actively been developed as electron sources replacing an electron gun for high definition, thin display apparatuses or as electron sources (emitter sections) of microscopic vacuum devices capable of high speed operation.
Conventionally, electron emitting devices of a xe2x80x9cheat emission typexe2x80x9d, by which a high voltage is applied to a material of tungsten or the like heated to a high temperature to emit electrons are used. Recently, electron emitting devices of a xe2x80x9ccold cathode typexe2x80x9d which do not need to be heated to a high temperature and can emit electrons even at a low voltage have actively been developed. Various kinds of electron emitting devices of the cold cathode type are available. In general, a field emission (FE) type, a tunnel injection (MIM or MIS) type, and a surface conduction (SCE) type have been reported.
In an FE type electron emitting device, a voltage is applied to a gate electrode to apply an electric field to an electron emitting section. Thus, electrons are emitted from a cone-shaped projection formed of silicon (Si) or molybdenum (Mo). An MIM or MIS type electron emitting device includes a stacking structure including a metal layer, an insulating layer, a semiconductor layer and the like. Electrons are injected from the side of the metal layer and caused to pass through the insulating layer, utilizing the tunneling effect, and the electrons are emitted outside from an electron emitting section. In an SCE type electron emitting device, an electric current is caused to flow in a planar direction of a thin film formed on a substrate, and the electric current is emitted from an electron emitting section-formed in advance (in general, a microscopic crack portion existing in an electricity-conducting area in the thin film).
The structures of these cold cathode type electron emitting devices all have a feature that a precision machining technology is used to. reduce the size of the structure and raise the integration degree.
A cold cathode type electron emitting device is required to provide a high level of electric current when driven at a low voltage and a low power consumption and is also required to have a structure: which can be produced at low cost.
As such a cold cathode type electron emitting device, Japanese Laid-Open Publication No. 7-282715, for example, discloses a structure schematically shown in FIG. 1. The conventional structure shown in FIG. 1 utilizes diamond, which obtains a negative electron affinity when subjected to a specific treatment, as an electron emitting source. The structure shown in FIG. 1 uses diamond particles, instead of a diamond film, in an attempt to simplify the production process and also to reduce the production cost.
More specifically, with reference to FIG. 1, a conductive film 112 to be formed into an electrode is formed on a substrate 111, and an electron emitting section 114 formed of diamond particles 113 is formed on the conductive film 112. The diamond particles 113 have a negative electron affinity as a result of a specific treatment. An electron extraction electrode (not shown) is provided opposite to the diamond particles 113 By supplying the electron extraction electrode with an electric potential, the electrons are emitted outside from the electron emitting section 114 formed of the diamond particles 113.
The electron affinity at the surface of the diamond particles 113 is negative. Accordingly, the electrons injected from the conductive layer 112 to the diamond particles 113 are expected to be easily emitted from the diamond particles 113. With the structure shown in FIG. 1, theoretically, it is expected that the electrons can be emitted outside without a high voltage being applied to the electron extraction electrode (not shown) opposed to the diamond particles 113.
The structure shown in FIG. 1, which uses the diamond particles 113 to form the electron emitting section 114, can be formed easily and at low cost.
Generally, an electron emitting section included in an electron emitting device is required to fulfill the features of, for example, (1) easily emitting electrons at a relatively small electric field (i.e., capable of efficient electron emission), (2) providing a satisfactorily stable electric current, and (3) having a small over time change in the electron emitting characteristics. However, the electron emitting devices as described above which have been reported so far have problems of a large dependency of the operating characteristics on the shape of the electron emitting section or a large over time change.
With the conventional technology, it is difficult to produce electron emitting devices at a satisfactory reproducibility, and it is very difficult to control the operating characteristics thereof.
In the conventional structure shown in FIG. 1, the following problems may actually occur when emitting electrons from the electron emitting section 114.
First, unlike the above theory, the electron extraction electrode (not shown) opposed to the diamond particles 113 forming the electron emitting section 114 needs to be supplied with a high voltage as in the conventional device, despite the fact that the electron affinity of the diamond particle 113 is negative. This is because of an electron barrier existing at an interface between the conductive layer 112 and the diamond particles 113. Such a problem does not occur when the conductive layer 112 and the diamond particles 113 form an ohmic contact, but it is generally difficult, in terms of materials, to obtain an ohmic contact between the conductive layer 112 and the diamond particles 113. As a result, a Schottky contact is formed between the conductive layer 112 and the diamond particles 113. In order for electrons to be injected from the conductive layer 112 into the diamond particles 113, the electrons need to go over the electron barrier existing at the interface between the two. Therefore, the electron extraction electrode opposed to the diamond particles 113 needs to be supplied with a high voltage as in the conventional device in order to emit the electrons outside from the diamond particles 113 forming the electron emitting section 114.
In the structure shown in FIG. 1, the diamond particles 113 need to adhere to the conductive layer 112 uniformly and stably in order to allow each diamond particle 113 to act as an electron emitting source and to realize uniform and stable electron emission. However, the uniform and stable application is difficult. Especially, the application stability is significantly influenced by the size of the diamond particle 113. When, for example, the particle size is on the order of microns, some of the diamond particles 113 may drop, which makes stable electron emission difficult.
As described above, with the conventional structure shown in FIG. 1, it is difficult to obtain an electron emitting device having fully satisfactory operating characteristics. The exemplary reasons are that it is difficult to efficiently inject electrons from the conductive layer 112 into the diamond particles 113, and that it is difficult to cause the diamond particles 113 to uniformly and stably adhere to the conductive layer 112 and thus to fix the diamond particles 113 to uniformly and stably to the conductive layer 112. For these reasons, the structure of the conventional electron emitting device and the structure and materials of the electron emitting section included in the conventional electron emitting device do not fully satisfy the required characteristics.
The present invention made for solving the above-described problems has objectives of (1) providing an electron emitting device capable of obtaining a large amount of current at low voltage driving and a method for producing the same; (2) providing a highly stable electron emitting device which can be produced at low cost and is capable of efficiently emitting electrons, by using particles containing a carbon material having a carbon six-membered ring structure or an aggregate of the particles for an electron emitting section; (3) providing an electron emitting device capable of more efficiently emitting electrons, especially by using, particles containing a carbon material having a carbon six-membered ring structure as the electron emitting material; (4) providing a highly efficient electron emitting source by providing a plurality of electron emitting device described above; (5) providing an image forming apparatus for displaying a bright and stable image, using the above-described electron emitting source and the image forming member; (6) providing a method for producing an electron emitting device for easily and efficiently carrying out an important production process which uses particles containing a carbon material having a carbon six-membered ring structure used as the electron emitting section; and (7) providing a method for easily producing an, electron emitting device having a stably operating electron emitting section over a large area with a satisfactory reproducibility, by carrying our the step of uniformly fixing particles containing a carbon material having a carbon six-membered ring structure onto an electrode.
In accordance with one aspect of the present invention, an electron emitting device including at least a first electrode and an electron emitting section provided on the first electrode is provided. The electron emitting section is formed of a particle or an aggregate of particles, and the particle contains a carbon material having a carbon six-membered ring structure. By this, the above-described objectives are achieved.
In one embodiment, the electron emitting device further includes a second electrode provided in the vicinity of the electron emitting section.
In one embodiment, the electron emitting section is fixed to the first electrode with a fixing material.
In one embodiment, the first electrode has a surface having a rugged pattern, and the electron emitting section is provided on the rugged pattern of the surface.
In one embodiment, the carbon material having a carbon six-membered ring structure has graphite as a main component.
In one embodiment, the graphite is highly oriented graphite.
Preferably, the electron emitting section is provided on the first electrode in a state where a portion at which a "sgr" bond of carbon six-membered rings is broken is directed in an electron emitting direction.
In one embodiment, the carbon material having a carbon six-membered ring structure has graphite as a main component, and the electron emitting section is provided on the first electrode in a state where the normal to a direction in which layers of graphite are laid is substantially parallel to a surface of the first electrode.
Alternatively, the carbon material having a carbon six-membered ring structure has graphite as a main component. The electron emitting section is provided on the first electrode in a state where the normal to a direction in which layers of graphite are laid is substantially perpendicular to a surface of the first electrode. A portion at which a "sgr" bond of carbon six-membered rings is broken exists on a top surface of the graphite.
In one embodiment, the carbon material having a carbon six-membered ring structure has a carbon nanotube as a main component.
For example, a tip of the carbon nanotube projects from a surface of the particle.
Preferably, a tip of the carbon nanotube is opened without being closed.
For example, the carbon nanotube is formed by refining bulk carbon containing a carbon nanotube generated by arc discharge between carbon electrodes.
Alternatively, the carbon nanotube is formed by a plasma CVD technique utilizing a catalyst.
Preferably, the fixing material is a vehicle.
In one embodiment, the first electrode includes an element which is capable of generating a carbon compound.
In one embodiment, the first electrode includes a multiple layer structure including at least one semiconductor layer.
In accordance with another aspect of the present invention, in an electron emitting device including at least a first electrode and an electron emitting section provided on the first electrode, the electron emitting section is formed of a particle or an aggregate of particles, and the electron emitting section is fixed on the first electrode with a fixing material. By this, the above-described objectives are achieved.
Preferably, the particle contains a carbon material having a carbon six-membered ring structure.
Preferably, the fixing material is a vehicle.
Preferably, the fixing material exists only in a portion of a surface of the first electrode at which the electron emitting section is fixed and does not exist in the remaining part of the surface of the first electrode.
In accordance with still another aspect of the present invention, in a method for producing an electron emitting device including at least the steps of forming a first electrode, and providing an electron emitting section formed of a particle or an aggregate of particles on the first electrode; a particle formed of a material containing a carbon material having a carbon six-membered ring structure is used as the particle. By this, the above-described objectives are achieved.
In one embodiment, the method further includes the step of providing a second electrode in the vicinity of the electron emitting section.
In one embodiment, the step of providing the electron emitting section includes the step of fixing the electron emitting section to the first electrode with a fixing material.
Preferably, a vehicle is used as the fixing material.
In one embodiment, the method further includes the step of forming a surface of the first electrode to have a rugged pattern, and the electron emitting section is provided along the rugged pattern.
For example, the rugged pattern is formed by a sand blasting technique.
Alternatively, the rugged pattern is formed by an etching technique.
In one embodiment, the step of providing the electron emitting section on the first electrode includes:
an application step of applying a solution obtained by mixing the particle in a prescribed fixing material onto a surface of the first electrode, and a drying step of drying the applied solution.
The application step can be performed by spinner application.
Preferably, by the drying step, the fixing material is removed from a part of a surface of the electron emitting section, the part being in the vicinity of an electron emitting site and including the electron emitting site.
In one embodiment, the method further includes the step of removing the fixing material at least from a part of a surface of the electron emitting section, the part being in the vicinity of an electron emitting site and including the electron emitting site.
In one embodiment, the step of providing the electron emitting section on the first electrode includes an application step of applying a solution which contains a particle forming the electron emitting device mixed therein onto a surface of the first electrode, and a treatment step of removing the solution at least from a part of a surface of the electron emitting section, the part being in the vicinity of an electron emitting site and including the electron emitting site, while forming a carbide between the electron emitting section and the first electrode. The electron emitting section is fixed to the first electrode with the carbide.
Preferably, the treatment step includes a step of exposure to a plasma containing at least one of hydrogen, oxygen, nitrogen, argon, krypton and hydrocarbon.
In accordance with still another aspect of the present invention, in a method for producing an electron emitting device including at least the steps of forming a first electrode, and providing an electron emitting section formed of a particle or an aggregate of particles on the first electrode; the step of providing the electron emitting section on the first electrode includes an application step of applying a solution obtained by mixing a prescribed fixing material and the particle forming the electron emitting section onto a surface of the first electrode, and a drying step of drying the solution so as to remove the fixing material at least from a part of a surface of the electron emitting section, the part being in the vicinity of an electron emitting site and including the electron emitting site. By this, the above-described objectives are achieved.
Preferably, a particle formed of a material containing a carbon material having a carbon six-membered ring structure is used as the particle.
Preferably, a vehicle is used as the fixing material.
Preferably, as a result of the drying step, the fixing material exists only in a portion of the surface of the first electrode at which the electron emitting section is fixed and does not exist in the remaining part of the surface of the first electrode.
An electron emitting source according to the present invention includes a plurality of electron emitting devices arranged in a prescribed pattern; and means for supplying an input signal to each of the plurality of electron emitting devices. Each of the plurality of electron emitting devices is an electron emitting device described above according to the present invention. The plurality of electron emitting devices each emit electrons in accordance with the input signal thereto. By this, the above-described objective are achieved.
An image display apparatus according to the present invention includes an electron emitting source described above according to the present invention, and an image forming member irradiated with electrons emitted from the electron emitting source to form an image. By this, the above-described objectives are achieved.
A method for producing an electron emitting source according to the present invention includes the steps of forming a plurality of electron emitting devices which are arranged in a prescribed pattern so as to emit electrons in accordance with an input signal to each of the plurality of electron emitting devices; and forming means for supplying the input signal to each of the plurality of electron emitting devices. Each of the plurality of electron emitting devices is formed by a method described above according to the present invention. By this, the above-described objectives are achieved.
A method for producing an image display apparatus according to the present invention includes the steps of forming an electron emitting source; and providing an image forming member, irradiated with electrons emitted from the electron emitting source to form an image, at a prescribed positional relationship with respect to the electron emitting source. The electron emitting source is formed by a method described above according to the present invention. By this, the above-described objectives are achieved.